Stabilizer for floating offshore drilling rigs



Sept. 29, 1964 E. J. BRINKMANN, JR.. ETAL 3,150,623

STABILIZER FOR FLOATING OFFSHORE DRILLING RIGS Filed Aug. 2, 1962 s Sheets-Sheet 1 I Fig. 1 [v f l6 L 34 L n m ,6 4 I4 34 32 12 Fig. 2 \v Emile .1. Br inkmann, Jr.

Henry W. Blake/y 1N VENTORJ' Sept. 29, 1964 E. J. BRINKMANN, JR.. ETAL 3,150,628

STABILIZER FOR FLOATING OFFSHORE DRILLING RIGS Filed Aug. 2, 1962 s Sheets-Sheet 2 i'i \v I Emile J Brinkmami. Jr:

Henry W. Blake/y INVENTORsS' Sept. 29, 1964 Filed Aug. 2; 1962 Fig. 7

STABILIZER FOR FLOATING OFFSHORE DRILLING RIGS 3 Sheets-Sheet 3 Fig. 8 Q

R 80 7i 9 "uni a? H Emile J Brinlrmann, Jr.

Henry M. Blake/y INVENTORS United States Patent 3,150,628 STABILIZER FUR FLOATING OFFSHORE DRHIJLING RIGS Emile J. llrinhmann, .lr., New Orleans, and Henry W.

Blalrely, Harahan, La., assignors to Zapata Offshore Drilling C0., Houston, Tex., a corporation Filed Aug. 2, 1962, 'Ser. No. 214,358 12 Claims. (Cl. 114-423) This invention comprises a novel and useful stabilizer for floating offshore drilling rigs and more particularly relates to a stabilizing device specifically adapted for mounting upon the hull of a vessel and especially the hull of the vessel intended for use in drilling offshore wells and which will to a large extent counteract the rolling of the vessel hull in response to waves of a height and wave length normally encountered in offshore well drilling operations.

The principal object of this invention is to provide a means for stabilizing the hulls of vessels to prevent or at least materially reduce the rocking of the vessel hull in waters having a wave motion lying in a predetermined range of variation as to the heights and spacing of the wave crests.

A further object of the invention is to provide a means whereby a vessel may be rendered substantially non-rolling for waves of a predetermined character as to height and spacing of wave crests.

A further object of the invention is to provide a stabilizer construction in accordance with the preceding objects which may be securely attached to vessels having a relatively narrow beam in order to render such vessels substantially non-rolling in seas having waves of a predetermined characteristic as to wave length and amplitude.

Still another object of the invention is to provide a stabilizing construction in accordance with the preceding objects which shall be capable of being readily attached to a vessel hull and which may be easily positioned in a horizontal and stabilizing position or in a lifted inoperative position for navigational purposes.

Another object of the invention is to provide a stabilizer in accordance with the above-mentioned objects which shall be of a unitary or prefabricated construction and of a chord-like truss construction to increase its rigidity and resistance to lateral flexing.

A further and more specific object of the invention is to provide a stabilizer construction specifically adapted for use in increasing the stability of a drilling platform for ofishore drilling operations and the like and which shall be capable of substantially eliminating or at least materially reducing the rolling action of such platforms in seas having waves of a predetermined range of Wave lengths and wave amplitudes.

A further object of the invention is to provide an apparatus in accordance with the preceding objects which shall convert a vessel having a hull of a relatively narrow beam and which would be insufiicient for use as a platform for offshore drilling operations to a vessel having a sufficiently increased resistance to rolling under wave action of a predetermined wave length and amplitude to enable it to function satisfactorily as a stable drilling platform.

Still another object of the invention is to provide a device in accordance with the preceding objects which shall be so constructed as to properly and inherently adapt itself and the vessel to which it is attached to prevent rolling in response to a predetermined magnitude of Wave length and wave amplitude.

Yet another specific object of the invention is to provide an apparatus in which a rigid outrigger assembly is employed to rigidly secure a buoyant body to a vessel hull at a distance which is so correlated to the amplitude and 3,159,628 Patented Sept. 29, 1964 length of waves of predetermined magnitude as to employ the wave action on the buoyant body as a means to counteract the rolling of the vessel hull by such wave action.

In offshore drilling barges and the like it is frequently desirable and necessary to position the drilling rig and its platform over the side of the vessel bull in order to facilitate the positioning of the rig over a well or its removal from the well, especially upon completion of the latter. However, the mass of the drilling rig in such over-the-side or off-center positioning of the rig frequently adversely affects the trim or stability of the vessel, especially under the influence of heavy wave action.

It is therefore a very important object of this invention to provide an outrigger type of stabilizer means which will effectively improve or overcome this condition and will beneficially affect the use of such over-the-side drilling rig installations, with or without inclusion of provision for compensating for waves of inordinate heights within predetermined ranges.

These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout, and in which:

FIGURES l6 show a preferred construction of a stabilizing arrangement in which FIGURE 1 is a frag mentary top plan view of a portion of a vessel hull and showing the stabilizer construction by which a pair of buoyant bodies are rigidly secured in a critically spaced relation to the hull;

FIGURE 2 is a front elevational view of the arrangement of FIGURE 1;

FIGURE 3 is a fragmentary perspective view taken from above and showing the stabilizer or outrigger construction attaching a buoyant body to one side of a vessel hull;

FIGURE 4 is a fragmentary detail view in vertical transverse section taken substantially upon the plane indicated by section line 4-4 of FIGURE 3 and showing certain details of the manner in which the stabilizer outrigger has its lower chord fixedly secured to the vessel hull and to the buoyant body;

FIGURE 5 is a perspective view of the upper chord of an outrigger stabilizer member;

FIGURE 6 is a perspective view of the lower chord of one of the stabilizer outrigger members at one side of the vessel hull;

FIGURE 7 is a fragmentary view in top plan showing a second embodiment of a stabilizer construction by which a buoyant body is secured to a vessel hull at one side thereof, this construction permitting selective raising and lowering pivoting movement of the stabilizer between a horizontal stabilizing position and a raised inoperative position to facilitate maneuverng of the vessel;

FIGURE 8 is a fragmentary detail view of one end of the construction of FIGURE 7;

FIGURE 9 is a detailed view in vertical transverse section taken substantially upon the plane indicated by sec tion line 9-9 of FIGURE 8; and

FIGURE 10 is a diagrammatic view indicating the dynamic principles of operation of the stabilizer assembly when two buoyant bodies are rigidly secured to a vessel hull by an outrigger assembly.

The basic purpose of this invention is to provide a stabilizer for the hulls of vessels which will substantially eliminate or materially reduce rolling of the hull in seas having waves within a predetermined selected range of magnitude and amplitude that is, of a predetermined Wave length and height of wave crest. The essence of the invention resides in the provision of one or more buoyant bodies which are rigidly connected to a vessel hull in a side-by-side fixed relation and which are spaced from the vessel hull by a distance which is so correlated to wave lengths and amplitudes within a predetermined range as to utilize the effect of these waves upon the buoyant bodies as a means to counteract the tendency of the vessel hull to roll under such waves, thereby producing a much more stable condition for the vessel hull. Although not limited thereto, a very important purpose of this invention and for which this invention is specifically well adapted is to render more stable the hulls of vessels of a relatively narrow beam and which would otherwise be unsuitable as a drilling platform for offshore drilling operations whereby such vessels are rendered capable of effectively serving that purpose.

As is well known, modern offshore drilling barges which are particularly adapted for drilling on the continental shelf in varying depths of water, are relatively large and costly vessels. When such vessels are entirely floating rather than being of the type having adjustable supporting legs by which the vessel hull is lifted above the water and above the reach of wave action, it is very difficult even with hulls constituting drilling platforms of a relatively great area, to maintain these platforms upon a sufiiciently level keel and stable condition such that drilling operations may be continued during wave action such as encountered during even mild storms.

However, such barges whether of the floating or of the elevated type are extremely difficult to move and difficult to maneuver. On the other hand, vessels having hulls of shallow beam such as offshore drilling barge tenders and the like while possessing the requisite mobility and maneuverability in moving to and from a drilling site, lack the necessary stability in themselves to constitute satisfactory drilling platforms. It is therefore the primary purpose of this invention to provide a stabilizer means which may be readily attached to vessels of relatively narrow beam to render them capable of serving as a satisfactory drilling platform while retaining their mobility and maneuverability.

In substantially all offshore drilling locations, the wave action during different weather conditions is fairly constant and predictable for such conditions. Thus, in mild weather wave actions are normally encountered with wave heights of about 4 feet. These pose no particular problem for offshore drilling barges. During heavy storms, such as during hurricanes when an extremely heavy wave action is encountered, all drilling operations are necessarily suspended. However, for weather conditions ranging between normal and less than that of a heavy storm wave actions of from 4 to 8 feet in height are frequently encountered. Heretofore, such wave actions have necessitated discontinuing of drilling operations upon floating drilling platforms and even upon some of the elevated drilling platforms which are supported by legs from the sea bottom, depending upon the depth of water in which they are operating. It is a further purpose of this invention to provide a stabilizer construction which may be applied to drilling platforms of all characters as Well as the hulls of vessels of relatively narrow beam and which will enable them to successfully withstand wave actions of this magnitude, that is, ranging from 4 to 8 feet wave heights, and will utilize by a proper spacing of buoyant members from the hull of the vessel, and properly timing the impact of the waves upon the buoyant bodies and upon the hull to produce a balanced effect which will substantially eliminate or reduce rolling action of the hull under waves during their subjection to waves of this magnitude.

In the accompanying drawings and set forth hereinafter as an exemplification of the principles of the invention and the manner of applying these principles to one form of practical utility, there is indicated by the numeral 10 a portion of a hull of a vessel which it is intended shall serve as a drilling platform for an offshore drilling rig such as that indicated generally by the numeral 12. It will be appreciated that this hull may be of various constructions and may be either a relatively narrow beam vessel such as that previously mentioned and which would otherwise be unsuitable for drilling operations, or may constitute in itself a drilling platform preferably of the floating type. Inasmuch as the stabilizer construction of this invention is in no way dependent upon the particular type of drilling rig or rigs carried by the hull or their location upon the hull, the representation of a drilling rig as generally indicated at 12 is deemed sufficient for the purposes of understanding the principles of this invention. As illustrated, this drilling rig may be located to one side of the vessel hull, or obviously any other location thereof may be employed and while only a single drilling rig is indicated, obviously a plurality of drilling rigs may be utilized.

In accordance with this invention, one or more buoyant bodies each indicated by the numeral 14 is positioned in a spaced side-by-side relation to the vessel hull 10 and are rigidly attached to the vessel -hull as by outrigger assemblies each indicated generally by the numeral 16. In the embodiments of FIGURES 1-6, the outrigger assembly and the stabilizing construction are rigidly connected to the vessel hull in a substantially permanent manner. However, in the modified form shown in FIG- URES 7-9, the stabilizer construction including the outriggers are pivotally connected to the hull for vertical tilting between a horizontally extending stabilizing position and a vertically elevated, inoperative position which will reduce the over-all width of the vessel to facilitate its maneuverability.

The buoyant body or bodies 14 may be of any suitable construction, and as illustrated may have pointed extremities and may have a propeller 18 powered from any suitable source such as an outboard engine or the like to facilitate the maintaining of the vessel hull in a desired position. However, the presence of the engine and propeller units are in no way necessary to an attainment of the basic purposes of this invention.

The buoyant bodies 14 are of sufficient flotation capacity to exert the necessary force for the stabilizing action as set forth hereinafter. An important feature of the invention resides in the critical spacing between the buoyant bodies and the vessel hull. Thus, as set forth hereinafter in connection with the diagrammatic view of FIGURE 10, the buoyant bodies are secured at a fixed distance from the hull such that the space between the longitudinal axes is correlated to the distance between wave crests of a predetermined amplitude, that is, of a height from 4 to 8 feet. Of course, if the stabilizing means is to be utilized to counterbalance rolling tendencies of the hulls to which they are attached in seas having wave crests outside of the range from 4 to 8 feet, obviously, a different fixed spacing corresponding to the selected range of Wave spacing and amplitude would be required.

In rigidly securing the buoyant bodies 14 to the hull 10 at the properly selected distance in accordance with this invention, the rigid outrigger assembly 16 is employed. In a preferred construction specifically intended as a prefabricated stabilizer outrigger assembly which may be subsequently attached to a particular vessel hull for producing the desired stabilizing effect thereon, the stabilizer outrigger assembly, see FIGURE 2, consists of a truss-like construction including an upper chord designated generally by the numeral 20 as shown in FIGURE 5 and a pair of lower chords each indicated by the numeral 22 as shown in FIGURE 6. As will be noted, the upper chord 20 extends across the vessel hull 10 and projects to both sides thereof to rigidly secure a pair of buoyant bodies 14 thereto. The lower chord 22 on the other hand, extends between one buoyant body and the adjacent side of the hull, there being two such lower chords required. Suitable bracing members rigidly connect the upper and lower chords together as shown in Z3 FIGURE 3. Thus a very rigid assembly is provided which may be readily secured to a vessel hull.

A preferred manner of suitably anchoring the outrigger assemblies to the vessel hull is shown in FIGURES 2 and 4. Here, the vessel hull is provided with a suitable substantially horizontal flat upper surface 24 and a substantially flat horizontal lower surface which extends outwardly beyond the upper surface as shown at 26. The upper and lower chords 20 and 22 respectively rest upon and are secured to the surfaces 24 and 26 in a manner to be now described.

Considering first the upper chord 20, it will be observed that this includes a continuous girder 30 having a central portion 32 adapted to extend across and rest upon the horizontal surface 24 of the hull as shown in FIG- URE 1. For this purpose, in applying the stabilizer assembly to an existing vessel hull, it may be necessary to rework and modify the hull superstructure in order to provide a clearance for receiving the member 32. The latter is welded or otherwise rigidly secured to the vessel hull, and has angulated end portions as at 34 extending to opposite sides of the vessel hull, which end portions in turn are each adapted to overlie a buoyant body 14. Diagonal transverse bracing rods 36 and 38, see FIGURE 3, together with the necessary intermediate bracing members 40 are rigidly attached to each of the angulated end portions 34 and projecting laterally therefrom are attached to the girders 42 which constitute the other edge of the top chord. As will be noted, these girders 42 have relatively short angulated adjacent end portions 44 which are adapted to rest upon the top surface 26 of the vessel hull and to be welded thereto or otherwise rigidly attached. These end portions may terminate short of such hull superstructure as the cabin structure 46.

It will thus be apparent that the upper chord is fixedly secured to the horizontal upper porion 24 of the vessel hull at positions spaced forwardly and rearwardly thereof and projects laterally to opposite sides of the hull for attachment to the buoyant bodies 14.

Each of the lower chords 22 consists of a pair of girders 50 having cutaway inner end portions 52 by which they are adapted to rest upon and be welded or otherwise fixedly secured to the horizontal lower surfaces 26 on the opposite sides of the vessel hull. A pair of transverse or diagonal brace rods 54 and 56 rigidly connect the two girders 50 together and through the aid of suitable braces as at 58 produce a rigid lower chord. The outer end portion of each of the girders 50 is likewise recessed or notched as at 60 to obtain a secure seating upon the top surface or a seating surface of the buoyant body 14 to which the lower chord may be fixedly secured as by welding or the like. The attachment of the lower chord to the body 14 is shown in FIGURE 4 in somewhat greater detail.

Suitable vertically extending brace rods as at 62, 64, 66 and 68, see FIGURE 3, extend between the various elements of the upper and lower chords for rigidly connecting the two chords together and to the buoyant bodies 14. Thus there is provided a truss-like rigid outrigger assembly of sufficient strength to rigidly and permanently secure the buoyant bodies 14 to the hull in a fixed spaced relation at the critical distance from the hull which is correlated to the wave height and length for which the stabilizing assembly is specifically designed.

In the construction just described, it will be understood that the stabilizer construction including the outrigger assemblies may be prefabricated and then subsequently applied to the vessel hull either with or without any necessary alterations of the hull structure.

Although the stabilizing assembly has been shown as consisting of two buoyant bodies each disposed at one side of the hull of the vessel, it will be appreciated that additional numbers of buoyant bodies may be utilized as may be desired. Further, it is within the purview of this in- 65 vention to utilize a single buoyant body disposed at only one side of the vessel hull.

As above mentioned, the spacing of the buoyant bodies from the vessel hull is critical and is correlated to the particular wave characteristics for which the stabilizing unit is desired. In general, the outrigger assembly will be of a minimum length to position the buoyant body at the minimum distance which is correlated and corresponds to the wave length and amplitude for which the stabilizing device is designed. However, it obviously would be possible and is within the purview of this invention to use a distance which is an integer multiple of the above-ment-ioned minimum distance and still obtain the desired stabilizing action.

Referring now to the embodiment of FIGURES 79, it will be observed that the vessel hull as indicated by the numeral 70 corresponds substantially to the vessel hull 10 and has the horizontal outrigger assembly upper and lower supporting surfaces 72 and 74 corresponding to the surfaces 24 and 26 of the preceding form. Further, the buoyant bodies 76 may be identical with the bodies 14 previously described and the outrigger assembly components 78 of the stabilizing means may similarly correspond to the assembly 16. Consequently, a detailed description of these components and their connection to each other is admitted as being repetitious.

However, in this form of the invention, instead of the rigid connection of the assembly 16 to the vessel hull, it will be understood that these assemblies have their outer ends rigidly connected to the buoyant bodies 76 in a manner previously described but they are pivotally connected to the vessel hull. Thus, the upper chord 80 and the lower chord 82 are pivotally connected to the vessel hull by pivot pins as at 84 and 86 respectively. Suitable power operating means, such as diagrammatically indicated by the hydraulic cylinder and piston units 88, see FIGURE 7, are connected to the upper chords 86 of the two assemblies 78 and to a suitable mounting on the vessel hull so that they may be utilized to effect a positive lifting or lowering of the assemblies 78 about their pivotal connections. For this purpose, the lower pivot 86 may be removed so that the entire pivoting action may occur about the pivot 84, with the pivot pin 86 being utilized merely to lock the assembly in its lowered and operative horizontal position.

By means of this construction, the stabilizing assemblies which may be prefabricated and applied to the hulls in the same manner as set forth in connection with the form of the invention of FIGURES 16, may be locked in the horizontal operative position for stabilizing the vessel, or may be selectively raised in a tilted position to reduce the over-all width of the vessel with its stabilizing means, so as to facilitate maneuvering of the vessel.

However, the operation of the stabilizing means in this form of the invention is identical with that previously described both as to structure and operation except for the above set forth differences.

Reference is now made to the diagrammatic view of FIGURE 10 for an understanding of the correlation between the stabilizer span and the height and spacing of wave crests in order to counteract rolling of the vessel hull.

In this diagram, A represents the vessel hull having its longitudinal axis about which it is prone to roll lying in a vertical plane coinciding with the arrow B. Stabilizing pontoons C and D are rigidly connected to the hull by the stabilizer or outrigger trusses E and F. The structure is assumed to be subjected to the action of a wave G which would cause a rolling action of the hull. By the use of pontoons, a lifting or lowering force, indicated by the arrows H and I is exerted upon the lever arms presented by the stabilizers E and F which force is transmitted to the hull tending to roll the latter.

When a wave crest I reaches a pontoon or the hull it lifts it as indicated by the arrows H and I. On the other hand, a wave trough K lowers the pontoon or hull to which it is applied as shown by the arrow B. The arrival of wave crests J at the pontoons C and D produce lifting forces H and I respectively which through the lever arms of the stabilizers E and F produce counterclockwise and clockwise moments respectively upon the hull. If the center of the hull is placed midway of the wave crests J, the two resulting moments will be equal and opposite resulting in their opposing each other and eliminating a tendency to roll. Consequently the stabilizers must be of a length which will position the associated pontoons at a half wave length from the bull, or an integer multiple of a half wave length.

It has been ascertained by tests that the height of a wave bears a fixed relation to the distance between crests, this distance being approximately twenty times the length. Therefore, to overcome the rolling tendency of 8 foot waves, a spacing of 160 feet between the pontoons C and D is necessary. In a similar manner the spacing required for waves of different heights can be determined.

In the foregoing description, the use of the pontoons as a means to prevent rolling has been emphasized. However, either with or without the critical spacing for this purpose, the pontoons and stabilizers have another very important function.

Considered solely from the aspect of obtaining optimum stability and trim, the location of the drilling rig on the longitudinal axis of the hull and operating the rig through a slot in the hull would be preferable. However, this poses serious problems in maneuvering the drilling rig over a well site for servicing operations and in moving the rig and vessel off of a completed well. Therefore an over-the-side location of the rig with respect to the hull is frequently desirable.

The offset location of the rig, however, introduces the factor of uneven distribution of weight which detrimentally affects the stability against rolling and the trim or list of the hull, especially in rough seas. This invention therefore envisions the use of pontooons and stabilizers as a means to overcome this last mentioned condition and restores the desired stability against rolling and the desired trim or list of the hull.

The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention as claimed.

What is claimed as new is as follows:

1. An offshore drilling barge comprising a vessel hull having a beam which is insuflicient in seas having a wave crest height lying within a predetermined range to afford the requisite stability of a drilling platform, a well drilling rig mounted upon said hull, a roll resistant stabilizer assembly secured to said hull and comprising a pair of buoyant bodies disposed in the water on opposite sides of said hull together with an outrigger construction attached to said hull and to said buoyant bodies and maintaining the latter in fixed spaced relation to said hull and at a distance from each other which is approximately twenty times said predetermined wave crest height and thereby cause said stabilizer assembly to exert a force on said hull from the wave action upon said bodies which will oppose and substantially balance the force simultaneously exerted by said wave action on said hull and thereby alford the requisite hull stability for drilling.

2. The combination of claim 1 wherein said predetermined range of wave crest height lies between about 4 to 8 feet.

3. The combination of claim 1 wherein said bodies are spaced apart approximately feet.

4. The combination of claim 1 wherein said outrigger construction includes an upper chord secured to an upper portion of said hull and a pair of lower chords each secured to one of said buoyancy bodies and to a lower and outwardly extending portion of the hull.

5. The combination of claim 1 wherein said outrigger construction includes upper and lower chords rigidly connected together, said upper chord having a mid-portion extending transversely across and secured to an upper portion of the hull and a pair of lower chords, each having an outer end fixedly secured to one of said bodies and inner ends secured to lower and oppositely laterally projecting portions of said hull.

6. The combination of claim 5 wherein said upper chord includes a first horizontal member extending from one of said buoyant bodies to the other and each of said lower chords comprises a horizontal member whose outer end is secured to the upper portion of one of said buoyant bodies.

7. The combination of claim 1 wherein said drilling rig is mounted upon said hull in an over-the-side overhanging relation.

8. The combination of claim 1 wherein said outrigger construction includes a single continuous horizontal member extending between and fixedly secured to both said bodies.

9. The combination of claim 1 wherein said outrigger construction includes a single continuous horizontal member extending between and fixedly secured to both said bodies, said member being disposed upon and fixedly secured to a top surface of said hull.

10. The combination of claim 1 wherein said outrigger construction includes a pair of trusses each connected to said hull and to one of said bodies, each truss comprising upper and lower chords rigidly connected and each pivoted to said hull for swinging movement of the associated body.

11. The combination of claim 1 wherein said distance between said bodies is an integer mulitple of said twenty times said predetermined range of wave crest height.

12. The combination of claim 1 wherein said pair of bodies are equidistantly spaced from said hull.

References Cited in the file of this patent UNITED STATES PATENTS 1,303,508 Simpson May 13, 1919 2,986,241 Fuller May 30, 1961 3,002,484 Dube Oct. 3, 1961 3,051,113 Swiger Aug. 28, 1962 FOREIGN PATENTS 493,503 France May 3, 1919 484,373 Italy Sept. 8, 1953 586,995 Canada Nov. 17, 1959 

1. AN OFFSHORE DRILLING BARGE COMPRISING A VESSEL HULL HAVING A BEAM WHICH IS INSUFFICIENT IN SEAS HAVING A WAVE CREST HEIGHT LYING WITHIN A PREDETERMINED RANGE TO AFFORD THE REQUISITE STABILITY OF A DRILLING PLATFORM, A WELL DRILLING RIG MOUNTED UPON SAID HULL, A ROLL RESISTANT STABILIZER ASSEMBLY SECURED TO SAID HULL AND COMPRISING A PAIR OF BUOYANT BODIES DISPOSED IN THE WATER ON OPPOSITE SIDES OF SAID HULL TOGETHER WITH AN OUTRIGGER CONSTRUCTION ATTACHED TO SAID HULL AND TO SAID BUOYANT BODIES AND MAINTAINING THE LATTER IN FIXED SPACED RELATION TO SAID HULL AND AT A DISTANCE FROM EACH OTHER WHICH IS APPROXIMATELY TWENTY TIMES SAID PREDETERMINED WAVE CREST HEIGHT AND THEREBY CAUSE SAID STABILIZER ASSEMBLY TO EXERT A FORCE ON SAID HULL FROM THE WAVE ACTION UPON SAID BODIES WHICH WILL OPPOSE AND SUBSTANTIALLY BALANCE THE FORCE SIMULTANEOUSLY EXERTED BY SAID WAVE ACTION ON SAID HULL AND THEREBY AFFORD THE REQUISITE HULL STABILITY FOR DRILLING. 